View Compilation Error

0_0_29760776_26032.cpp: In function 'void build(int, int, int)':
0_0_29760776_26032.cpp:40:8: error: 'lson' was not declared in this scope
  build(lson);
        ^
0_0_29760776_26032.cpp:41:8: error: 'rson' was not declared in this scope
  build(rson);
        ^